The present invention relates to the packaging of opto-electronic chips, and more particularly to the packaging of an opto-electronic chip containing surface normal opto-electronic devices.
In an opto-electronic chip package, an opto-electronic chip is attached to a second level electronics package (e.g., a circuit board, etc.). The opto-electronic chip consists of one or more opto-electronic devices (e.g., photodetectors, quantum well modulators, semiconductor lasers, etc.) that are typically mounted on a semiconductor chip. The opto-electronic package further includes an optical fiber sub-assembly that receives one or more optical fibers and fixes them in a specific angular and positional orientation for optical communication with the opto-electronic device(s).
Often, the opto-electronic devices on the opto-electronic chip are surface normal opto-electronic devices. Such devices emit or receive an optical signal along an optical axis that is perpendicular to the top (or bottom) surface of the device. One common example of a surface normal device is a vertical cavity surface emitting laser.
FIG. 1 depicts surface normal opto-electronic chip package 100, which includes chassis 102, circuit board 112, opto-electronic chip 128, optical fiber sub-assembly 134 and heat sink 138, interconnected as shown.
Chassis 102 includes first portion 104 and second portion 106 that are perpendicular to one another. Circuit board 112 includes chip-receiving region 114 and motherboard-interfacing region 116 that are separated by flexible region 118. Chip-receiving region 114 receives opto-electronic chip 128 and motherboard-interfacing region 116 includes electrical connections 122 to motherboard 132. Opto-electronic chip 128 includes surface normal opto-electronic devices 130 and optical fiber sub-assembly 134 includes optical fibers 136.
Optical axis 1xe2x80x941 of optical fiber sub-assembly 134 (and optical fibers 136) is substantially perpendicular to the emitting/receiving surface of the surface normal opto-electronic devices 130 on chip 128. Also, it is desirable for axis 1xe2x80x941 of optical fiber sub-assembly 132 to be substantially parallel to motherboard 132 (shown in phantom) upon which package 100 is mounted. (In FIG. 1, axis 1xe2x80x941 is not parallel to motherboard 132 because, for clarity, chip receiving portion 114 of circuit board 112 is not depicted in its final position against first portion 104 of chassis 102.)
To obtain these positional relationships, flexible circuit board 104 is advantageously used. Its use allows placing chip-receiving region 114 in perpendicular relation to motherboard-interfacing region 116. This is accomplished by flexing flexible region 118 that is disposed between chip-receiving region 114 and motherboard-interfacing region 116 of circuit board 104.
To maintain this perpendicular relationship, chip-receiving region 114 and motherboard-interfacing region 116 of flexible circuit board 104 are typically attached to rigid xe2x80x9cL-shapedxe2x80x9d chassis 102. Usually, fasteners 140 (e.g., machine screws, etc.) are used to attach motherboard-interfacing region 116 to second portion 106 of chassis 102. Fasteners 140 are received by threaded openings 120 (in motherboard-interfacing region 116) and threaded openings 110 (in portion 106 of chassis 102). Fasteners 142 are used to attach chip-receiving region 114 to first region 104 of chassis 102. Fasteners 142 are received by threaded openings 124 (in chip-receiving region 114) and threaded openings 108 (in portion 104 of chassis 102).
Additionally, heat sink 138 must be attached to chip-receiving region 114 of circuit board 112 to withdraw heat that is generated by attached opto-electronic chip 128. Fasteners 144 can be used for this purpose. Fasteners 144 are received by threaded openings 146 (in heat sink 110) and threaded openings 126 (in chip-receiving region 114).
As a consequence of attaching the circuit board 112 to chassis 102, and heat sink 138 to the circuit board, chip-receiving region 114 has a disadvantageously high fastener count. A high fastener count can lead to low reliability and, further, requires area to be dedicated to the fasteners that could otherwise be used for electronic circuitry, etc.
Accordingly, there is a need for an improved opto-electronic chip package that avoids disadvantages of the prior art.
The aforedescribed need is met by a chip package in accordance with the present invention. A chip package in accordance with the illustrative embodiment of the invention comprises a rigid L-shaped chassis to which a flexible circuit board is attached. The flexible circuit board includes a chip-receiving region, which receives an opto-electronic chip having surface normal opto-electronic devices disposed thereon. The flexible circuit board also has a motherboard-interface region that provides electrical connection to a motherboard. A flexible region is disposed between the chip-receiving region and the motherboard-interfacing region. When in position against the chassis, the chip-receiving region and the motherboard-interfacing region are perpendicular to one another.
An optical fiber sub-assembly places a plurality of optical fibers in optical communication with the surface normal opto-electronic devices. An optical axis of the optical fiber sub-assembly is perpendicular to an emitting/receiving surface of the surface normal opto-electronic devices. The optical axis of the optical fiber sub-assembly is parallel to the motherboard-interface region of the circuit board.
The chip package further includes a housing that receives the chassis, the circuit board and the optical fiber sub-assembly. Before placing the chassis, circuit board and optical fiber sub-assembly in the housing, the motherboard-interfacing region of the circuit is attached to the chassis. By virtue of the flexible region of the circuit board, as the chassis and circuit board are placed in the housing, the chip-receiving region of the circuit board is forced against the chassis. The chip-receiving portion is advantageously maintained in this position without the use of machine screws, etc.
The housing has an opening to allow a heat sink to be attached to the chip-receiving region of the circuit board to remove heat that is generated by the opto-electronic chip. The same fasteners (e.g., screws, etc.) that are used to attach the heat sink to the circuit board also advantageously attach the circuit board to the chassis, minimizing screw count in the circuit board.